Oil filter
An oil filter removes particles from oil , which is mostly used in closed circuits. The best-known design consists of a housing, usually made of deep-drawn metal, and the actual filter, consisting of a nonwoven or a woven fabric .
Since an oil filter creates a pressure drop, the oil must be forced through the filter by a pump . The filter is therefore usually located directly behind the pump in the circuit. One speaks here of a so-called "main flow filter". In the suction line in front of the pump there is u. U. a coarse sieve to protect the pump. This is, for example, the usual arrangement in motor vehicle engines and also in aircraft engines. In aircraft engines there is a coarse filter (sieve) in front of each lubrication point to protect against built-in dirt (possibly also chips from production). It is also possible to install the filter in the return line, where the pressure is lowest and so that the housing of the filter can be built as lightly and cheaply as possible. That depends on the use case and the security principals. For safety reasons, oil filters (main flow filters) are provided with a bypass valve in order to maintain operation with unfiltered oil in the event of a filter blockage and to prevent the filter from bursting. In aircraft engines, the pressure drop across the oil filter is continuously monitored and the replacement required for maintenance purposes is then determined.
Filters in combustion engines
Internal combustion engines are lubricated with oil. The heat during combustion also burns parts of the oil. In order to maintain the lubrication of the machine, burnt parts of the oil, metal debris and other dirt (e.g. soot ) are filtered out in the oil filter. The filter in the motor vehicle is replaced periodically, typically every year or every 10,000 to 30,000 kilometers, depending on the manufacturer's specifications for the car . In the case of aircraft engines, the filter housing is cut open and a check is made to see whether chips have accumulated. Chips are a sign of dangerous wear and tear .
Commercially available disposable oil filter for vehicles
Oil filter insert for cars
Schematic of the oil filter
Bypass filter
The bypass flow filter is either arranged parallel to the main flow oil filter or in a continuous separate circuit, which is equipped with its own pump. As a result, only part of the oil flow rate flows through the oil filter (5% - 10%) and the pore size can be reduced to such an extent that the smallest impurities can be filtered. Depending on the application, the effectiveness of bypass filters in internal combustion engines with regard to extending the oil service life is controversial.
Microfilter
A variant that is occasionally retrofitted in the motor vehicle sector is the microfilter in a bypass arrangement. A certain part of the oil is permanently pressed directly from an oil pan or the like through a second filter without flowing through the engine. The finer bypass flow filter can filter out particle sizes of up to 0.1 µm, whereas main flow filters have channel widths of around 5–10 µm. The main advantage is that condensation is removed from the oil. There are also concepts that work exclusively with a filter in the bypass flow. For reasons of environmental protection, the use of biogenic oils is increasingly sought. However, since the oil is not only burdened by pollution, but also ages due to oxidation and the loads occurring in the engine (heat, shear forces, etc.) and the additives in particular have a limited service life, a prolonging influence on the oil change intervals is controversial.
Centrifuge oil filter
Another concept for oil filtering in the bypass flow is that of centrifugation. This principle is currently increasingly used, especially in trucks. The oil pressure is used to drive a Segner fluid wheel (after Johann Andreas von Segner ) similar to a dishwasher or lawn sprinkler. As the oil passes through the filter, it is subjected to high centrifugal forces, which results in the separation of soot and other small particles of pollution, the density of which is greater than that of the oil. With centrifuge oil filters, microscopic air bubbles can also be specifically removed from the oil, which otherwise could have a very negative effect on the lubricating properties: Due to their lower weight, they collect in the center, where they combine and burst.
Filters in oil heating systems
Oil filters are also used in oil heating systems and have to be replaced at maintenance intervals. Different types of filters are offered (paper, felt or plastic filters).
Filters in hydraulic systems
Oil filters are also used in all hydraulic systems. A distinction is made between two different reasons for filtering:
Function protection filtering
The filtration is only aimed at removing coarse dirt that would interfere with the function of the machine due to jamming or clogging. The filters used are usually quite coarse. Mostly, surface filters such as B. wire screens used. These filters are used in simple and little-used hydraulic systems, e.g. B. jacks and car lifts .
Anti-wear filtering
To protect against wear, very fine filters are used in order to remove as many particles as possible that can cause abrasion. Depth filters are used almost exclusively to remove foreign bodies from 1/1000 mm in size. These filters are used for expensive and complex hydraulic systems: excavators , injection molding machines , machine tools , presses , construction machinery , tunnel boring machines , agricultural machines and the like. Ä.
Individual evidence
- ↑ Oelcheck GmbH: Do partial flow filters keep what they promise? (Section: Conclusion). Retrieved January 8, 2013 .
